The outer rearview mirrors of a vehicle, as important accessories for observing vehicles or pedestrians behind are important elements to facilitate safe driving, and enable the driver to observe a particular field of view by the adjustment of the angles. The importance of the outer rearview mirrors is universally acknowledged. Normally the folding device is electrically driven to avoid the inconvenience of driving in a narrow space or colliding with the pedestrian or vehicle damage caused by unnecessary dispute in complex occasions since the outer rearview mirrors are mounted on the two sides of the vehicle. The electric folding, device is generally rotatably mounted between the mirror substrate and the mirror support fixed on a vehicle to achieve the folding function. In order to reduce the frictional resistance between the mirror substrate and the mirror support when folding, a certain gap is reserved between the two when the electric folding device is designed. The problem is that, the lower end surface of the mirror substrate lacks support by the mirror support due to the gap, and the mirror substrate is solely supported by a pin shaft for folding, and tightly pressed by the spring sleeve-mounted on the pin shaft, during driving, especially when driving fast or on bumping roads, shaking may occur as the poor anti-shudder capability. In addition, the gap may cause large wind noise, and the mirror substrate and the mirror support are all injection-molded with plastic material, which is prone to aging after a long-time use, meanwhile, other factors such as the inclusion of wind or sand, the resistance caused by rotation may occur, with a high operational current, phenomenon of folding failure may take place.